The former royal editor of the News of the World warned his managing editor that if payments to his confidential sources were traced, they and the editor would be jailed, the phone hacking trial heard on Thursday.

In an email to Stuart Kuttner, which was forwarded to Mr Kuttner’s personal assistant, Beverley Stokes, Clive Goodman discussed the contacts that he paid in cash. Two were “in uniform” while the third worked at a rival newspaper and was therefore taking a serious risk, the jury at the Old Bailey was told.

The email of July 2005, which was shown to the jury, read: “Morning, Stuart. Understand that, as you know, there are only three people I ever pay in cash.

“Two are in uniform and we — them, you, me, the editor — would all end up in jail if anyone traced their payments. They’ve had Special Branch crawling all over them since we ran a five-par story about an Operation Trident [Scotland Yard’s murder investigation unit] arrest at Clarence House. Thanks to the way we pay them, they’re untraceable.

“The third is an executive at another newspaper who is also taking on potentially life-altering risks for us and will not accept any other form of payment.’’